Higher combustion and exhaust temperatures may be exhibited during higher engine loads and/or boosted engine conditions. These higher temperatures may increase nitrogen oxide (NOx) emissions and cause accelerated degradation of catalytic materials in the engine and exhaust system. Exhaust gas recirculation (EGR) is an approach to combat these effects. EGR strategies reduce an oxygen content of intake air by diluting it with exhaust. When the diluted air/exhaust mixture is used in place of ambient air not mixed with exhaust gas to support combustion in the engine, lower combustion and exhaust temperatures are exhibited. EGR also increases fuel economy in gasoline engines by reducing throttling losses and heat rejections.
To enable appropriate control of EGR dilution levels and maintain combustion stability, the EGR is homogenized with intake air via an EGR mixer, in some examples. One example approach is shown by Vaught et al. in U.S. Pat. No. 8,056,340. Therein, an annular EGR chamber is located annularly around an annular protrusion, which restricts a cross-sectional flow through area of an intake passage. The EGR chamber is fluidly coupled to a narrower portion of the intake passage where a vacuum may be formed to promote EGR mixing with intake air.
However, the inventors herein have recognized potential issues with such systems and have devised a series of approaches to address them. As one example, portions of intake air may flow through the annular protrusion without mixing with EGR. This may lead to poor EGR distribution, which may result in increased emissions and decreased combustion stability.
In one example, the issues described above may be addressed by a mixer comprising a hollow, annular ring having a first chamber fluidly coupled to an EGR passage and a second, separate chamber fluidly coupled to an intake passage via inlets located on a downstream surface and where the first and second chambers are fluidly coupled at an outlet located along an intersection between an upstream surface and the downstream surface adjacent to a restriction of an intake passage. In this way, EGR and intake gases combine before flowing to the intake passage.
As one example, the outlet is located along a portion of the intake passage where the mixer creates a greatest restriction. In this way, a vacuum may draw EGR and intake air from the first and second chambers, respectively, through the outlet, and into the intake passage. The second chamber is configured to receive gases at a location downstream of the outlet. As such, unmixed intake air (e.g., intake air free of EGR) and/or an intake air/EGR mixture may circulate through the mixer after flowing passage the outlet. This may increase a likelihood of mixing EGR with intake air. As such, distribution of EGR to each of the cylinders of an engine may be more uniform.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.